I have a class 6... doesn't make to much difference. The main performance lags are the file size (or lack of) and the fact that the default encoding (h264) is just to hard for the processor to compile effectively.
You should still modify the build.prop file. The BB mod/file doesn't switch the video to m4v or up the file size enough. Here are the settings I used:
Higher Quality Video Recording | Root Your Droid
The most noticeable difference between the class 2 and 6 (for our purposes) is in transferring large amounts of data (eg. I have 14G of music on it). IF we ever get the ability to run apps from the SD card then this will be a bigger issue.